Pictures aren't great, it decided to fly to the bottom of the wheelie bin when I went back out with my camera. Been through some pics of hoverflies and wasps on G00gle images but can't seem to find it.

Just found out its name. It's a ichneumon xanthorius. Apparently the ichneumon species made a lot of people doubt the existence of God, including Darwin, due to it eating the caterpillars during its larval stage.

It's certainly an Ichneumon wasp, but you can't id these from photographs: the 3000 or so species that we have in the British Isles converge on a small number of colour patterns, even across families. The only place these lay eggs is inside larvae of moths, butterflies and sawflies.